<template>
    <ul class="list">
        <li 
        class="item" 
        v-for="item of letters" 
        :key="item"
        :ref="item"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
        @click="handleLetterClick">{{item}}</li>
    </ul>
</template>

<script>
    export default {
        name: 'CityAlphabet',
        props: {
            cities: Object
        },
        computed: {
            letters () {
                const letters = []
                for (let i in this.cities) {
                    letters.push(i)
                }
                return letters
            }
        },
        data () {
            return {
                touchStatus: false,
                startY: 0,
                timer: null
            }
        },
        updated () {
            this.startY = this.$refs['A'][0].offsetTop
        },
        methods: {
            handleLetterClick (e) {
                //console.log(e.target.innerText)
                this.$emit('change', e.target.innerText)
            },
            handleTouchStart () {
                this.touchStatus = true
            },
            handleTouchMove (e) {
                if (this.touchStatus) {
                    if (this.timer) {
                        clearTimeout(this.timer)
                    }
                    this.timer = setTimeout(() => {
                        const touchY = e.touches[0].clientY - 57
                        const index = Math.floor((touchY - this.startY) / 23)
                        if (index >= -2 && index < this.letters.length) {
                            this.$emit('change', this.letters[index])
                        //console.log(index)
                    }
                    }, 16)  
                }
            },
            handleTouchEnd () {
                this.touchStatus = false
            }
        }
    }
</script>

<style lang="stylus" scoped>
  @import '~@/assets/styles/varibles.styl'
  .list
    display : flex
    flex-direction : column
    justify-content : center
    position : absolute
    top : .08rem
    right: 0
    bottom : 0
    width : 1.4rem
    .item
        line-height :1.44rem
        text-align : center
        color : $bgColor
</style>